What you need: Apple iPhone, $199; CalcPad App, $1

Risk level: Medium

Convincing your professor or teacher to let you use your iPhone as a calculator will more than likely end up with him or her telling you FOH! However, on the off chance that your teacher is cool with you using your smartphone as a calculator, we recommend using the CalcPad app. On top of being a calculator, CalcPad lets you store notes and even surf the Web.